/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    int minDepth(TreeNode* root) {
        int ret=0;
        queue<TreeNode*>q;
        if(root)q.push(root);
        while(q.size())
        {
            ret++;
            int sz=q.size();
            while(sz--)
            {
                auto node=q.front();
                q.pop();
                if(!node->left&&!node->right)return ret;
                if(node->left)q.push(node->left);
                if(node->right)q.push(node->right);
            }
        }
        return ret;
    }
};
